Pivoted implements having elongated members disposed for cooperative engagement about a pivotable joint are widely used by those desiring to transmit a force through the pivotable joint to a working piece engaged by the working surfaces of the implement. More particularly, pivoted tools such as scissors comprise two elongated members, typically made of stamped or forged metal or other suitable material, disposed for cooperative engagement about a pivotable joint. To facilitate operation of the implement by the user, handles conforming to the fingers or hands of the user have been molded onto the force applying end of each elongated member.
As is well known, the pivotable joint in most of such implements commonly comprises a rivet loosely passing through registered apertures in the members. Typically, to adjust frictional engagement of the members of such riveted tools production personnel must carefully strike the rivet with a suitable impact tool. Accordingly, to facilitate functional adjustment by production personnel after those implements are assembled, as well as to allow adjustments by the user after extended use of such tool, some of these implements are provided with a screw loosely passing through an aperture in one of the members and threaded into an aperture of the other member to maintain suitable friction between the pivoted members. In each of these instances, however, the assembling of such pivoted tools requires production personnel to bring the apertures formed in the separately manufactured elongated members into registration to install the rivet or screw that will maintain those members in assembled relationship, and subsequently adjust the friction between the members to the desired amount.
It has been found, however, that adjustable pivoted implements of the kind described above do not typically retain their frictional adjustment, because the fastener tends to loosen slightly with each operation of the implement. This deficiency has already been recognized and addressed by those skilled in the art and more particularly by those skilled in the scissors art. U.S. Pat. No. 2,626,460 to Wahl discloses a pair of scissors in which the hinge member is designed to enhance the durability of the frictional adjustment between the pivoted members. In such a device, two elongated members having metal blades and plastic handles are joined by a fastener threaded into a plastic boss formed integrally with one of the plastic handles and extending into the registered apertures formed in the elongated members. Although the metal to plastic bearing relationship in items of this type tends to decrease the frequency with which such scissors must be adjusted, conventional assembling operations are typically necessary in the production of such improved scissors, i.e., separately manufactured elongated members are assembled by bringing into registration the apertures formed in each member.
In the manufacture of pivoted tools such as scissors, cutting edges are ground at the working end of each member or suitable working surfaces are formed at such working ends. As explained above, if desired, each of such members is then provided with a handle of molded plastic or other suitable material preferably ergonomically conforming to the fingers or hand of a user. Such molding operation conventionally consists of positioning an elongated member in a suitable space in a die casting mold wherein the member is fixed in position with respect to the mold by means of a pin or the like which goes through the aperture in the member and which is secured to the mold surfaces. As described in U.S. Pat. No. 4,715,122 to one of the present inventors, that space communicates with a mold cavity for the handle portion, the cavity being subsequently filled with a fluid plastic material or the like, whereby the plastic material partially surrounds the force applying end (also called tang portion) of the elongated member so that the handle is molded onto the tang. The same operation is separately repeated to form the handle on the other elongated member.
As already explained above, the final step in manufacturing scissors or other pivotable tools, whether elongated members of such items have earlier been provided with molded handles, consists of bringing the apertures of the two elongated members into registration and installing the pivot member to maintain them in cooperative assembled relationship about the pivotable joint.
As is generally known and as is more particularly described in U.S. Pat. No. 4,715,122 to one of the present inventors, due to manufacturing tolerances, the position of the aperture in each of the elongated members with respect to the extremity of the working end, i.e., the tip in the case of scissors, and with respect to the working surface, i.e., the cutting edge of the blade of scissors, varies within certain limits. This means that the distance between the center of the aperture and the tip of a scissor blade as well as between the center of the aperture and the cutting edge of the blade varies from blade to blade.
These manufacturing variances manifest themselves in the assembled item in two characteristic ways easily recognizable by those skilled in the art. First, in pivoted tools or scissors assembled in accordance with the method identified above (i.e., by bringing the apertures in the blades into registration), it often turns out that certain other portions of the working surfaces of the tool are not in desired registration when the tool is in a closed configuration. More specifically, some portions of the working ends may protrude to a different extent in the direction of the longitudinal axis of the pivoted tool. In the case of scissors, this means that the tip of one of the blades may extend beyond that of the other blade. To correct this defect, a first manual finishing operation will be required after the pivoted tool is assembled. This operation normally consists of grinding the protruding working end to match the length of the associated working end to achieve required longitudinal registration of the working ends, in the case of scissors, longitudinal registration of the tips of the scissors.
Second, it is also well known to those skilled in the scissors art that proper operation of scissors requires a certain amount of rotational overlap when the scissors are in a closed configuration. However, manufacturing tolerances necessary to permit production of such items at reasonable costs will also tend to create some variance in how the stop face of one elongated member engages the abutment face of the other member, or the abutment face of the plastic handle of that other member if the tool is provided with plastic handles. Such variance will also tend to undesirably affect the amount of rotational overlap and consequently impair the operation of the scissors. Correcting this rotational overlap problem typically requires a second manual finishing operation consisting of adjusting the engagement of such stop face and abutment face to obtain the desired amount of rotational overlap.
Problems resulting from manufacturing tolerances of pivoted tools have already been recognized and addressed by those skilled in the art. U.S. Pat. No. 4,715,122 to Linden discloses a pair of scissors having metal blades and plastic handles in which the plastic pivot member (the hinge pin) of each scissor half is formed as part of a tongue of the plastic handle which is molded to the scissor half using the tip of the scissor half as reference point. As disclosed in U.S. Pat. No. 4,715,122, one way to resolve this misalignment is by fixing the tip of the blade in the mold so that the distance between the tip of the blade and the hinge member is always the same, because the tip and the bearing surface provided for the hinge member in at least one tongue are determined by the mold. The portion of the pin that is positioned in the hole of one scissor blade has a diameter equal to that of the hole while the portion positioned in the hole of the other scissor blade has a smaller diameter than the hole, thereby allowing for misalignment of the blades. Although this approach alleviates some of the problems associated with these expected manufacturing variances, items of the type disclosed in Linden still require that each plastic handle with corresponding pivot member be formed separately and each scissor half be subsequently assembled.
From the foregoing, it can be readily recognized that prior art methods used to manufacture pivoted tools having elongated members, such as scissors or the like, typically require assembling two members which have previously been entirely manufactured separately and, due to necessary manufacturing tolerances, at least two manual finishing operations once such items are assembled. It can therefore be appreciated that in addition to increasing the cost of such pivoted items, these finishing operations will also tend to undesirably affect uniformity of appearance, and possibly consistent operation, of these items.
Thus, it is desirable to provide pivoted tools such as scissors or the like which can alleviate the problems associated with conventional manufacturing methods, i.e., which do not require the two finishing operations described above, and which are engineered to lend themselves to automatic functional assembling.